Strongbox is a free open source app for human rights and privacy activists to be able to record video with their phones without having to worry about the device being lost or seized, although in some countries you can be charged for not revealing your password to law enforcement.
The app is really simple to use, when you launch it for the first time you will be prompted to compose a passphrase to locally encrypt the videos, if you forget the passphrase, all data will be unrecoverable and lost.
Straight away after login you enter the video mode with two big buttons at the bottom of the screen, the one represented by a camera logo starts the recording when tapped, the other button represented by a memory card logo gives you access to the video library.
Stored videos have timestamps next to them, you can view the video on your phone, delete it or upload it to a server. Strongbox gives an internal IP address where the video should he uploaded, I found it confusing, being an internal IP many people will not realise it is their own computer IP, another thing is that when you erase a video no confirmation is asked for and files can be deleted by mistake.
Footage is encrypted on the fly as you film, files never touch the memory card, videos are stored inside the encrypted container in Strongbox. The encryption algorithm used is AES256bit in GCM mode, this provides confidentiality and integrity, a lock allows you to instantly close down the app preventing access to the videos with one tap.
I would use this app to keep my own videos private and not much more, I found the sharing options lacking, that is a problem if your phone is seized. An oppressive law enforcement agency will not be able to view the recordings but you will have lost access to what could be indispensable footage of abuse, I wish there was an easy way to quickly get the videos out of the phone.
This is a basic app with basic functions using standard encryption that can be checked for bugs and backdoors, probably useful to keep video clips of your girlfriend intended for personal viewing encrypted.